Engine systems with spark ignition modules may be configured to achieve peak power outputs to meet engine operating requirements. In inductive spark ignition engines, an ignition coil may provide the necessary spark energy to effect the spark plugs to ignite a homogeneous air-fuel mixture in the combustion chamber, causing engine rotation. The ignition coil includes a primary winding and a secondary winding. One end of the primary winding is connected to a battery (e.g. 12 V DC) wherein high peak current steadily flows from the battery through the primary winding of the coil to establish an electromagnetic field in the ignition coil core, while the other end is connected to a switching mechanism. The tip of the spark plug contains a gap that the voltage must jump across for sparking to occur. In order to actuate a spark plug for ignition, the switching mechanism is disconnected, thereby rapidly collapsing the magnetic field within the primary winding and inducing a high voltage current in the secondary winding of the ignition coil, which is connected to a spark plug. The high voltage in the ignition coil produces spark energy (e.g. produces a spark) across the gap between spark plug electrodes to ignite the air-fuel mixture for combustion.
The spark energy provided by the ignition coils results from the time that current flows through the ignition coil. The time during which current flows within the ignition coil or in other words, the period of time for which the ignition coil is charged is termed dwell or dwell time. The energy of the ignition spark may directly influence engine performance wherein an ignition spark with low energy resulting from reduced dwell time may cause unreliable combustion. On the other hand, high spark energy and longer spark duration may be effective at preventing engine misfiring and may be obtained with higher dwell times. However, while high current supplied to the ignition coil may yield high spark energy with longer spark duration during high engine speed and load conditions, the high current supply may also contribute to premature wearing of the spark plug gap through electrode burn, increasing the spark plug gap size and increasing overall wear of the ignition system. Further, at low engine speed and load conditions, it may become necessary to provide longer spark duration to ensure ignition, which may again necessitate high current flow through the ignition coil for higher dwell, leading to increased wear of the ignition system.
The inventors herein have recognized potential issues with the above approach and provide a method to control an ignition system, with which the service life of spark plugs may be increased and ignition system wear may be decreased. As one example, the required dwell (e.g., required current supplied to the ignition coil) may be a function of the spark plug gap size wherein, at a given speed/load of the engine, a relatively new spark plug with smaller gap size may require less current to breakdown a relatively smaller spark plug gap as compared to the end of life spark plugs with a relatively bigger gap size. Selecting a dwell time based on engine operating conditions, if not adjusted to accommodate variation in the spark plug age and gap size seen over time, may negatively affect power output and engine performance. In light of these issues, it may be desirable to have an improved control of dwell time proportional to spark plug age and spark plug gap size such that ignition system wear may be reduced.
In one example, the issues described above may be addressed by a method for an internal combustion engine comprising adjusting spark plug dwell based on engine operating conditions, and further adjusting the spark plug dwell in proportion to existent spark plug conditions to derive an adjusted spark plug dwell time controlling a supply of current to an ignition coil. In this way, dwell time may be calibrated as warranted by engine operating conditions and may be further calibrated proportional to spark plug age and spark plug gap size, at a given time. As one example, scalar factors are applied to a baseline dwell time based on both engine load/speed and spark plug gap size to produce an increased dwell time when spark plug age/gap size is high and engine speed/load is high, or when spark plug age/gap size is low and engine speed/load is low.
The present disclosure may offer several advantages. By adjusting dwell time responsive to engine speed and load, premature wear of spark plugs may be effectively reduced and life of the spark plugs may be extended. Additionally, by further adjusting dwell time proportional to spark plug age and spark plug gap size, overall electrical energy consumption may be decreased leading to reduced heating and aging of the ignition coil, thereby reducing component stress, the rate of wear and extending the life span of ignition system components. Worn out spark plugs often incur deposits on spark electrodes known as spark plug fouling. Fouling of spark plugs may prevent a spark from breaking down the gap between spark plug electrodes for ignition to occur. By slowing down in the rate of wear of spark plugs by adjusting dwell, spark plug fouling may be prevented as well. In this way, overall wear of the ignition system and its components may be prevented.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.